TOKYO — Prime Minister Shinzo Abe of Japan won a crucial vote in the House of Representatives on Tuesday on an anti-conspiracy bill that he said was needed to fight terrorism but that critics feared could give the authorities broad surveillance powers over citizens.

With protesters gathered outside the country’s lower house of Parliament in Tokyo, Mr. Abe’s party and its allies approved a bill that would make it a crime to conspire with others to commit terrorism and a raft of other crimes.

Speaking before the vote, Hiroshi Hiraguchi, a member of the governing Liberal Democratic Party, expressed condolences for the victims of a suicide bombing that killed 22 people at a concert in Britain on Monday. He said that the bill was needed to help Japan fulfill “the grave responsibility” of hosting the 2020 Olympics in Tokyo.

Mr. Abe’s party called for the vote even as a United Nations expert on human rights accused the government of rushing the measure without sufficient debate on appropriate safeguards for privacy and free speech.

Joseph Cannataci, the United Nations special rapporteur on the right to privacy, wrote to Mr. Abe warning that the bill, if adopted, could “lead to undue restrictions to the rights to privacy and to freedom of expression.”

A day before the lower house voted, Mr. Abe’s chief cabinet secretary, Yoshihide Suga, lashed out against Mr. Cannataci’s letter, calling it “clearly inappropriate” and dismissing the special rapporteur’s concerns. The Japanese government also lodged an official protest with the Office of the United Nations High Commissioner for Human Rights.

Recent polls show the Japanese public is split over the anti-conspiracy bill, but more than three-quarters said the government had not sufficiently explained why it needed to pass the legislation. The bill is expected to go before the upper house of Parliament for final passage before the current legislative session ends in mid-June. Mr. Abe’s party and its allies have a two-thirds majority in both houses.

In an email, Mr. Cannataci said the government should take more time to discuss and amend the bill to include more safeguards for privacy and freedom of speech.

“This is the time for the government of Japan to sit back for a minute, reflect, realize that it can do things in a better way and then proceed to behave like a world-class democracy by taking the time necessary” to modify the bill, he wrote.

In a country where terrorism is extremely rare, critics say that the bill is far too vague in defining terrorism and that the list of crimes subject to possible surveillance was arbitrary.

An appendix to the bill includes unlicensed bike racing, copyright infringement and stealing plants from forest preserves, exposing those involved in the planning of such activities to prosecution.

Such crimes, critics say, seem to have little to do with terrorism. They say the bill would merely give the government wide latitude to put people under surveillance.

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Prime Minister Shinzo Abe of Japan voted on the anti-conspiracy bill in the House of Representatives on Tuesday.CreditAgence France-Presse — Getty Images

“There are no apparent reasons certain crimes are covered and others are not,” said Koichi Nakano, a political scientist at Sophia University in Tokyo.

Mr. Nakano said that because people might be worried about the government trawling emails, text messages and social media posts for evidence of criminal conspiracy, anyone who protests government policies might be reluctant to speak out.

“There will be more self-censorship in a country where there is already not a very vibrant civil society,” he said.

Although Japanese law requires the police to obtain warrants to install wiretaps on phones, the courts almost always grant such requests.

As a result, opponents of the bill say that it could strip citizens of their rights to privacy in the name of preventing terrorism. Japan has had few major terrorist attacks since 1995, when members of a cult killed 13 and sickened more than 5,800 in a sarin gas attack on the Tokyo subway.

“How far are we willing to sacrifice our privacy is the question,” said Kenta Yamada, a journalism professor at Senshu University in Tokyo. “We may possibly get into the world of ‘1984,’” he said, referring to the dystopian novel by George Orwell in which citizens are constantly under surveillance.

Concerns about the bill were stirred during testimony by Japan’s justice minister, Katsutoshi Kaneda, when he gave examples of the kinds of activities that might cause the authorities to suspect that an individual or group was planning a crime. In one instance, Mr. Kaneda suggested that someone visiting a park with a map and binoculars could be suspected of plotting a terrorist attack.

“It’s so vague that it allows the police to justify whatever they do,” said Kanako Takayama, a professor of criminal law at Kyoto University. “If you buy a pair of scissors, that may be viewed as preparing for a crime.”

But supporters of the bill said the opposition and the news media had inflated the justice minister’s comments rather than focusing on the content of the bill. “They just enjoy picking up the funny things of the minister who cannot explain things very well,” said Keijiro Kimura, a lawyer in Osaka who supported the bill.

Speaking in Parliament on Tuesday, Mr. Hiraguchi, the lawmaker, said that the bill was explicitly limited to “organized crime groups.”

“It is further clear that common people will not be the target of punishment stipulated by this legislation,” Mr. Hiraguchi said.

But the United Nations special rapporteur, Mr. Cannataci, said in an email that the bill was “defective.”

“With great power comes great responsibility,” Mr. Cannataci wrote. “Yet this bill is not accompanied by a stiffening of measures intended to safeguard privacy. Other rights like freedom of speech and freedom of association are likewise not reinforced.”

Opposition lawmakers said that the governing party had stifled debate and that the legislation needed more public input.

The Japanese people deserve to “decide for themselves where they want their freedoms restricted in order to protect their security,” said Shiori Yamao, a member of the opposition Democratic Party.

A version of this article appears in print on , Section A, Page 6 of the New York edition with the headline: Anti-Conspiracy Bill Advances in Japan. Order Reprints | Today’s Paper | Subscribe